The Herring Run

News and Information about the
 July 2017

In This Issue
Turtley Awesome Interns Continue Search for Diamondback Terrapins
Alarmingly Low Dissolved Oxygen Recorded in Herring River
Wheaton College interns Keaton Schrank, Kira Olander and James Marcucella studied diamondback terrapin population trends with Professor Emerita Barbara Brennessel. 

FHR Annual Meeting To Address 
Salt Marshes & Climate Change

6 pm, Tues. 8/15

Wellfleet Council on Aging
715 Old Kings  Highway

Herring River 101:
The Effects of Tidal Restriction and Restoration

Only one session left!

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Turtley Awesome Interns Continue Search for Diamondback Terrapins
For the past seven years, Wheaton College has conducted studies to monitor diamondback terrapins in the Herring River Estuary.  This summer, three Wheaton interns hiked along Chequessett Neck Road and on the paths adjoining the salt marsh in the Cape Cod National Seashore, looking for signs of this elusive turtle.
The diamondback terrapin (Malaclemys terrapin) lives in salt marshes and is listed as a "threatened" in Massachusetts.  The Herring River is the northernmost range of this species in the U.S. We are interested in learning how terrapins use the habitat on both side of the dike.  By conducting head counts and by monitoring nesting activity, we've developed a clear picture of terrapin movement and reproduction in the estuary.  Nesting has been documented on Griffin Island, along the Gut, on Great Island and even Chequessett Neck Road. It's no surprise that terrapin activity is concentrated near the extensive salt marsh on the seaward side of the dike. With salt marsh restoration, the habitat for terrapins is expected to expand.  Hopefully, this increase in nesting and foraging habitat will be beneficial to the survival of this species in the Herring River.

Alarmingly Low Dissolved Oxygen 
 Recorded in Herring River
For 108 years now the dike has blocked tides and seawater from the 1100-acre estuary upstream.  Nevertheless, most of the organic matter that accumulated within this expansive wetland over thousands of years remains.

Meanwhile, oxygen-rich Cape Cod Bay water, which would normally flood the river and creeks on every high tide, is greatly restricted by the dike at Chequesset Neck Road.  

In summer, decomposition of this organic matter puts a serious strain on the river's dissolved oxygen budget.  Indeed, during periods of low light for photosynthetic oxygen production, i.e. nighttime or cloudy weather, the river can be poised for complete oxygen depletion; the latter has been observed since at least the mid-1980s, accompanied by fish kills, in 1985 wiping out the entire juvenile river herring run when they attempted to journey from the kettle ponds to the sea.  This has likely been going on for the past 100-plus years, severely damaging aquatic habitat throughout the flood plain, and perhaps explaining the apparent abundance of nuisance mosquitoes.  Mosquito larvae and pupae don't require dissolved oxygen (they breathe air) and thrive in the absence of predatory estuarine fish.

The graph below shows dissolved oxygen trends from last summer (2016), collected by the US Geological Survey.  The yellow box encompasses the concentration range that is chronically stressful to fish and other aquatic animals that "breathe water"; the red box marks the range that is acutely lethal to aquatic life.  Oxygen varies with tides: the little bit of seawater that enters the river at high tide boosts dissolved oxygen, but during every low tide oxygen plummets as the water column becomes dominated by oxygen-depleted river water.
The second graph shows very recent data.  On nearly every low tide in summer the river water becomes highly stressful to fish and other aquatic animals.  (Imagine being in a room without air.)  The problem will continue, quietly and lethally, until the river is re-connected with the marine environment.

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